1. Field of the Invention
The present invention relates to multi-line wireless telephone systems and, in particular, to techniques for saving power in battery-operated wireless handsets in wireless telephone systems.
2. Description of the Related Art
The use of telephones and telephone systems, including wireless telephone systems, is widespread. In wireless telephone systems, a cordless or wireless telephone handset unit communicates via either analog or digital radio signals with a base unit, which is typically connected via a standard telephone line to an external telephone network. In this manner, a user may employ the wireless handset to engage in a telephone call with another user through the base unit and the telephone network.
Multi-line wireless telephone systems are also in use in various situations, such as businesses with many telephone users. Such systems employ a handset that communicates with up to N handsets simultaneously, typically with digital communications schemes, such as a spread-spectrum, time division multiple access (TDMA). In a TDMA system, a single RF channel is used, and each handset transmits and receives data during a dedicated time slice or slot within an overall cycle or epoch. Efficient power use is important for a wireless system since the handsets are typically battery-powered.
Previous power-saving and other TDM-type arrangements for battery-powered devices are described in U.S. Pat. No. 4,964,121 (Moore), issued 16 Oct. 1990; U.S. Pat. No. 5,150,361 (Wieczorek et al.), issued 22 Sep. 1992; and European Pat. App. no. EP 0 726 687 A1 (Nokia Mobile Phones Ltd.), published 14 Aug. 1996. The Moore patent describes a TDM system in which the communication channel is divided into a predetermined number of time slots, wherein a remote communication unit may communicate with a central control station within an assigned time slot. Moore describes battery saving circuits of individual radios which may synchronously monitor centrally transmitted synchronization signals at their respective predetermined assigned time slots, but otherwise be in a substantially unenergized power saving mode of operation. The Wieczorek et al. patent describes a TDM system in which batter powered communication devices operate in energy saving mode to shut down nonessential circuits for a predetermined time interval, awaking to monitor one of two control slots of a repetitive time frame structure. The Nokia reference describes a radio telephone system in which the telephone maybe placed in an active condition during a polling burst but in sleep condition at other times.
A wireless telephone system comprises a base unit having a base transceiver, and one or more wireless handsets, each handset comprising a handset transceiver. Each handset establishing a time-division multiple access (TDMA) link over a shared RF channel with the base unit via the base transceiver in accordance with a TDMA epoch, which allocates exclusive data and audio packet time slots to each handset. Each handset powers on its transceiver during its respective data and audio packet time slots as necessary to synchronize with the base unit using synchronization data transmitted with a data packet, to detect incoming call data transmitted with a data packet, or to transmit and receive audio information over the TDMA link. The handset powers off its transceiver otherwise during the epoch to minimize handset power use.